Surface water bodies in the form of lakes, ponds, reservoirs, rivers, and canals offer an abundance of resources generally beneficial to human and animal populations as well as to a variety of plant and marine species. Nevertheless, the presence of excessive nutrient levels within the water body can have a profound impact on those that depend on and make use of the resource unless corrective mitigative measure are implemented, at least on an interim basis to allow continued, uninterrupted use of the resource.
Lakes for instance may serve as an aesthetically pleasing setting; a fresh water supply; an ecological habitat for aquatic or marine life; a recreational area for boating, swimming, and fishing; and means for irrigation and storm-water control. The availability of the resource in terms of water quality, however, may be unduly compromised by the introduction of nutrients in the form of nitrogen and/or phosphorus that can disrupt the delicate ecological balance and unwittingly allow the surface water body to progress towards a eutrophic (nutrient rich) state from an oligotrophic (nutrient poor) state that is generally characterized as having little to no aquatic plant growth with commendable water clarity.
Although most water bodies start out in an oligotrophic state, human activities may accelerate the successional process or expedite the rate of eutrophication when higher amounts of nutrients are introduced to the water body from a variety of sources, such as deteriorating septic systems, sewer overspill, urban storm water runoff transporting detergents, fertilizers, and organic matter, and atmospheric deposition from industrial sources and automobiles. While the presence of phosphorus is relatively rare in lakes and ponds, human sources can overburden the water body with excessive amounts of phosphorus to the extent of serving as a food source for plants and algae and undesirably increase the vegetation growth within a lake, particularly along the shallow area around the shore of the lake defining the littoral zone where an adequate amount of sunlight is available for sustaining growth of rooted plants (macrophytes).
Algae are microscopic plants that grow naturally in lakes and ponds but are capable of adapting to a wide spectrum of aquatic conditions. Algae are photosynthetic yet lack vascular tissue such as roots and leaves and are considered to be evolutionarily less advanced than higher plant life, such as macrophytes. Algae are the primary producers in the aquatic environment and provide a source of food and energy for other animals. Additionally, during photosynthesis, algae release oxygen into the water column, making it readily available for consumption by living aquatic organisms.
Even though algae constitute an important part of the water body's ecosystem as mentioned above, a rapid growth of their population due an excessive concentration of phosphorus can create a condition called an algal bloom. Algal blooms can form scum or dense mats on the water body's surface and may also affect water color, odor and taste. During an algal bloom the excess algae die while the decomposition process consumes oxygen. This may result in an anoxic or oxygen-depleted condition, which is harmful or fatal to some aquatic animals and organisms. Diatoms and blue-green algae cause the most common algal blooms. Diatoms affect the color of the water such to turn it bright green or brown, but rarely create an offensive odor or scum and may even occur undetected to the casual observer. Conversely, blue-green algal blooms rarely go undetected. The force of wind can concentrate blue-green algae (cyanobacteria) into dense, unsightly surface mats, or surface scum, which may wash up along the shoreline while producing a noxious odor as it undergoes decomposition. Some species of blue-green algae, such as Anabaena aphanizomenoides, produce toxins that may be harmful to humans and wild and domestic animals that come into contact with the unsightly substance, whereupon such exposure to humans in particular may induce stomach pains, vomiting, diarrhea, skin or throat irritation, allergic reactions, breathing difficulties, skin rashes, and nerve and liver damage. Although most blooms are not toxic, toxicity is hard to predict. A single species of algae can have toxic and non-toxic strains and a bloom that tests non-toxic one day can become toxic the next day.
Though vegetation in the form of rooted plants and algae are considered an important part of any aquatic system given their capacity to produce oxygen in some instances, there are times when excessive amounts of aquatic vegetation can unduly interfere with the use of the resource. Aquatic vegetation, which had previously grown in unused or undeveloped areas, suddenly presents a problem to recreational users and riparian owners. Prolific growth of aquatic vegetation, particularly along the shoreline of the water body, may bring about problems in the nature of fouled outboard motor props, snagged fishing lines, a declining fishery, uninviting swimming conditions, diminishing aesthetic appeal, and falling property values. In addition to the toxicity of some strains of algae, algae in general can create slippery, hazardous conditions on boat ramps and docks to bring about safety concerns as well as furthering conditions of fish kills caused by die-offs of algal blooms that reduce the amount of available oxygen to living aquatic organisms. Moreover, heavy vegetation growth within swimming areas can impede or obscure swimmers. Offensive odors, pests and the negative perception of “unclean” water at areas of aquatic vegetation growth become uninviting, unsafe, and underutilized if mitigative measures are not implemented to preserve the water body's recognized resource, at least on a localized basis.
While most aquatic problems primarily occur during warmer conditions, colder climatic conditions during winter months equally present a challenge to the resource, notably in the nature of winterkill. Winterkill mainly occurs when snow and ice pack generously cover the water body to the extent of limiting the amount of sunlight reaching the aquatic plants, whereupon the amount of oxygen produced by the aquatic plant is observably reduced. If the aquatic plant dies from the lack of sunlight, the plants start to decompose, which uses oxygen dissolved in the water column, and when oxygen depletion becomes severe enough, fish die. The prolific growth of aquatic vegetation during summer months can account for most of the organic matter undergoing decay during the winter months. A lake bottom comprising an abundance of vegetation is more likely to experience winterkill than a lake lacking such materials and can contribute to the accumulation of decomposing vegetation over time to form a layer of muck about the lake bottom.
Although the ultimate mitigative measure for mitigating growth of aquatic vegetation involves the control of nutrients to the water body from identifiable point sources, it's not always immediately possible due to time and economic constraints. Accordingly, it is desirable to mitigate the prolific growth of aquatic vegetation and spread of algae on a provisional basis within areas generally recognized for use by riparian owners while widespread, long-term control measures are being set in place using best available technologies.
Some of the most common conventional methodologies for short-term implementation, at least from the perspective of maintaining continued use of the water body's resource along the shoreline, involve the mechanical removal of vegetation through harvesting, raking, and cutting; application of chemicals or dyes; localized nutrient deactivation; dredging; water circulation with aeration; or a combination of two or more of these methods. While each of the above methods have merit of affording a short-term solution, some better than others, their adaptation may not always constitute a practical economical solution. For example, mechanical removal may be effective for small areas of filamentous algae and aquatic vegetation growth but is time consuming and labor intensive when controlling larger areas, particularly upon the presence of filamentous algae that has the propensity to grow back rather quickly and may move around the water body through persistent wind and wave action. Further, chemical application in the form herbicide treatment, for example, may be beneficial in controlling a select species of unwanted vegetation growth, but can have a profound impact on the continued use of the resource by human and animal populations. Shading products in the form of dyes can be equally effective in limiting vegetation growth by reducing the amount of sunlight that reaches them if the concentration is maintained at adequate levels, which may be difficult at times given the uncontrolled movement of the water body through wind action and natural circulation. Similarly, dredging can be effective in some respects to deepen an abnormally shallow shoreline such to limit the amount of sunlight reaching the aquatic vegetation present about the lake bottom. On the other hand, water circulation that effects to aerate the water column can be moderately effective in controlling the growth and accumulation of unwanted weeds and algae during warmer and colder climatic conditions. Besides adding oxygen to the water column, aeration with circulation can destratify the layers existing at different temperatures so as to maintain a uniform, consistent oxygen level relatively about the water column during warmer and colder conditions, improve the decomposition of organic matter, moderate the amount of suspended material that generally leads to localized discoloration, reduce offending odors caused by anaerobic conditions, and cause suspended material to fall to the bottom of the lake where bacteria can break it down.
Accordingly, it is desirable to provide an apparatus that is economically viable in maintaining continued, localized use of the resource by moderating the amount of unwanted growth of aquatic vegetation and presence of toxic and non-toxic strains of algal on a sufficient basis that would otherwise be detrimental to the health of human and animal populations and aquatic organisms.